Swimming pools and spas typically operate in conjunction with a water recirculation system which is used for filtering the water in the pool and spa. Such recirculation systems often also are used in conjunction with chemical dispensing devices for dispensing chemicals, such as chlorine and other chemicals, into the pool. Most such systems do not continuously operate the pool recirculation pump, but rather, cause the pump to be operated for a pre-established period of time on a repeating cycle, usually every twenty-four hours.
The use of a control system which turns on the pump motor or the recirculating pump for pre-established periods of time during each twenty-four hour time interval (or other suitable interval) permits the pool recirculation and chemical addition to be effected during times of non-use of the pool. This is particularly desirable in conjunction with self-cleaning pools, which use "pop-up" heads located in the pool floor, since it is desirable to have all such heads recessed whenever the pool is in use.
The length of time the recirculating pump for the pool is operated for each of its operating cycles typically is set by the pool owner, without any scientific determination. For pools which are operated with relatively warm pool temperatures, it is been found, usually by trial and error, that a longer cycle of operation of the recirculating pump is required than at times when the pool water temperature is colder. In the southwest, for unheated pools, the difference is significant between summer operation (with relatively warm pool water) and winter operation (with relatively cold pool water). The pool operator usually manually adjusts the duty cycle of the operation of the recirculating pump arbitrarily, at various times of the year. Obviously, if the adjustment is not properly made, the recirculating pump may operate for a far longer duty cycle or time period in the winter than is necessary; or, conversely, the recirculating pump may be operated for much less than a desired length of time in warm weather.
It is desirable to provide a pool recirculation system which automatically adjusts the length of time of operation of the duty cycle for the recirculating pump in conjunction with the actual temperature of the water recirculated through the system.